Pathology Handbook

Heparin Monitoring (APTT)

Synonyms

APTT, APTT Ratio

Clinical Indications

Monitoring of unfractionated heparin therapy.
Note: for patients on low molecular weight heparin see Anti-Xa assay

Request Form 

Request via ICE

Availability

Daily

Specific Criteria

Patient should be bled with minimal stasis

Patient Preparation

Patient should ideally be at rest

Turnaround Time

Same day.

Specimen

Fresh citrated Blood; sample must be received by the laboratory within 4 hours of collection.

Volume

4.5 ml

Container

Blue capped vacutainer tube

Vacutainer blue top

Collection

Clean venepuncture. Samples must be received by the laboratory within 4 hours of collection

Causes for Rejection

Underfilled, clotted, haemolysed or if sample is too old.

Reference Range

An APTT ratio of 1.5 - 3.0 equates to a therapeutic heparin dose (0.2 to 0.5U heparin / mL plasma